Disclaimer: I don't own Hunter x Hunter or Undertale, obviously:p

Note: Gon and Killua are both at yorknew city arc level because I want to emphasize fights involve strategy a lot more. This fact could definitely change later on, but for now it is as it is.

'Hunter'= Thoughts

Hunter= Normal

Hunter= Narrative

*Hunter= Audible noise

OoO= Short cut/break XxxXxxx= Long cut/break

Chapter 1: Humans x and x Monsters

Long ago, two races ruled over Earth: Humans and Monsters

One day, war broke out between the two races

After a long battle, the humans were victorious

They sealed the monsters underground with a powerful inscription

Many years later...

Dark, looming clouds blotted out the sky and painted dark gray swirls over the once vibrant blue atmosphere. Gon sat in silence at the edge of the cave's mouth, watching absent-mindedly as the rain came thrashing down, waiting for it to finally let down, even a little.

Killua, meanwhile, busied himself kicking rocks into a seemingly bottomless pit covering the majority of the cave's surface. Although he was mad at Gon for choosing this cave of all caves, he soon grew to have no problem with it. 'Just how far does this pit extended,' "...Hey Gon," No answer, he sighed then raised his voice. "GON!"

"Huh?" Gon muttered, still mesmerized by the rain.

"C'mere, you have to check this out."

Gon stood up and walked over to Killua who was effortlessly holding a boulder twice his size in one hand while the other seeped into a pocket. "What?" Gon asked.

Killua slammed the boulder inside the pit and crouched down, Gon followed, he turned towards his friend, looking skeptically at Killua's intent face. "Come on, tell me what you're doing already."

"I realized while I was kicking rocks into this pit that none of them made a sound since I kicked it in. So I figured a giant boulder would do the trick, with the strength I exerted on that thing it should it the bottom in no time."

"Oooh, that sound cool!"

"Yep, now we wait."

OoO

"..."

"..."

"Killua, I think this pit's bottomless, we've waited ten whole minutes and nothing's happened."

"That's impossible, it's just a really long, deep pit. Tch, let's go the rain's already beginning to let up, there's no use in wasting more time...Gon, Gon, are you even listening?" Killua got his answer when Gon started dipping his head inside the pit in an attempt to get a closer range. "Jeez Gon, don't be stupid, you're going to fall down if you keeping doing that."

"I probably will, but you'll catch me so I don't need to worry!"

Killua simply smiled at Gon's easy going attitude, it was that attitude that kept them going throughout their adventures and never ceased to amuse Killua. "Do whatever you want then, I'm—"

*CRACK

XxxXxxx

"KILLUA!"

Gon sprung up, despite being in an otherworldly environment the only thing on his mind was Killua. He frantically searched around the childlike room bathed in a dry hue of scarlet; no sign of him.

Gon jumped off the bed, not even begging to question how he ended up in a bed in the first place and scurried to the door. Right before Gon could grasp his clammy palms on the knob, the door swung open. "...Killua!" Gon breathed a sigh of relief and returned to his usual calm state of mind.

"Oh hey Gon, took you long enough to wake up."

"Hey, do you know where we are?"

"It's a long story but-"

"Ah! Killua, do you smell that?! It smells super good!"

Gon pushed past Killua and ran in the direction of the delectable scent tugging at his nose. He breezed through several beige tinted rooms, only stopping when he reached the kitchen. 'Huh is that person a...' After pulling a pie out from the oven, the 'person' turned around and emitted a soft laughter as Gon scrambled to get out of sight.

"You can come in if you like, child."

Being one of those voices you couldn't say no to, Gon crept inside the kitchen and got a good, long look at her. In every way, shape, and form she was a literal goat with wiry, milk white fur and floppy ears falling down her face to accommodate. But, her contrastingly sharp horns, fangs, and crimson red eyes set Gon on the edge.

"You're a...goat?!" Gon blurted out.

She laughed. "Kind of, my name is Toriel, and I am the caretaker of these Ruins."

"Ruins?!"

"Yes, why don't we talk over a slice of pie?"

"Okay!" Gon hopped out the kitchen and approached the small table where Killua already seated himself. "I would've been if you hadn't jumped in and saved me like that," Killua said as Gon sat down.

"I didn't think about that, I saw you falling and I just kind of...moved."

Killua pulled off a petal from the bouquet of flowers sitting on the table. "So that's your excuse? Thanks to you and your moving we're both stuck down here."

"Y-yeah you're right," Gon sheepishly remarked. "But at least we're stuck down here together!"

He pulled off another petal. "W...whatever...speaking of this place, while you were still out I walked around her house and read some of her books, they're all about snails by the way, but I didn't see anyone else in here but us."

"In this big place? She must get pretty bored without anyone around..."

"It is rather boring," Toriel admitted, setting down two pie slices on the table. "But you get used to it after awhile...a long while." She happily watched the two boys gobble down their pie slices, it felt like ages since she was able to make pie for someone other than herself. "It's been a very long time since another human has fallen down here in the Underground."

"Most humans tend to stay away from deep, dark pits, unless you're Gon." Killua teased.

"You were the one who started throwing rocks in there!"

"Hey, I wasn't the one who stuck my entire head in there."

"I had to so I could hear the rocks fall down at the bottom."

'So that's where those rocks came from, interesting.'

"Just admit it was stupid, Gon."

"It wasn't stupid!"

The two glared at each other before breaking off in laughter. Killua pushed away his cleaned plate and looked at Toriel who was clearly enjoying their company. "Say Goat lady, can we go look around outside for a little bit?" Killua asked.

"Yeah! I wanna see where we are!" Gon dittoed, scooting off his chair and heading to the door.

"WAIT! DON'T GO!" Toriel's sudden outburst from her usual calm, soothing voice immediately caught the attention of Gon and Killua. They both spun their heads around to see Toriel's distressed face, from the looks of it, Killua could tell she never raised her voice like that before.

"I mean..." Toriel quickly spit out. "Let me come with you."

"Alright,"

"Yeah, you didn't have to ask."

The three left the closed comforts of Toriel's home and into the barren wasteland of the ruins. Gon's laced green boots scraped against the loose, purple dirt as he ran towards the giant black tree in front of her house.

He separated a pile of cherry red leaves scattered around the tree and fluffed them up like a pillow. "Watch this guys!" Gon hollered, climbing up the monochrome tree.

"You really shouldn't jump from that height!" Toriel called out. She ran towards Gon in a frenzy while Killua noticeably lagged behind.

"Don't worry, Gon'll be fine, he's got a really hard head," Killua said. "It'll take a lot more than—"

"OWWOWWW!"

"Human!"

Gon stood up, sorrowfully rubbing the back of his head. "Are you ok, human?! Where does it hurt?!"

He lifted his head and stuck his tongue out. "Haha, I'm just kidding!"

"Ha, see, what did I tell you? Gon wouldn't die even if he was thrown off a cliff."

Gon and Killua's joyful laughter was infectious among Toriel, despite how angry she was, she couldn't help but laugh along with them. 'These humans...'

"Hey, Toriel, I just remembered," Gon drew out. "You never told us anything about the Ruins." Gon raised his arm, his finger pointing at the hollowed out exit past the black tree. "There's more out there past this, right?"

"Yes, everyday I go back and forth between my house and those bed of flowers in hopes of seeing if a human fell down. Usually I walk back home disappointed, but today I found you two lying unconscious on the bed of flowers..."

"I thought you were dead at first, but when I saw several rocks and boulders lying around with blood smeared all over them I figured you were just knocked out and I took you two all the way back here." Toriel explained, she found herself back to old habits when her fingers started fumbling with each other. "However, going through that way, you'll only find yourselves back where you started."

"...beyond the Ruins there is an expansive world filled with monsters like myself, being humans, some will try to kill you so you shouldn't worry about what lies past this place."

"But that sounds really fun! I want to see the other places not just the Ruins, I mean, we'll be stuck down here for a while, might as well have fun!"

"I...I won't ever let you leave these Ruins...it's too dangerous for children like yourselves to venture out there."

"The how about this. If me and Killua can go all the way to the spot where we fell and comeback here in an hour then will you let us go?"

Toriel stared at Gon's face in shock. "Maybe I'll consider it if you're strong enough to do that..." She lowered her voice enough so they wouldn't hear. "Maybe then you won't die like the others..."

"Gon's just being modest. Together, we could do it in half an hour." Killua quipped.

"If only, but no, the Ruins is filled with brute monsters, and hazardous puzzles. Strength alone can't help you, you'll also need wit. I should also add that all monsters, regardless of circumstances, will always be born a conjurer, keep that in mind as you go since the monsters who fight you will know Nen."

'If that's the case, then this might actually be fun.'

"Oh, I almost forget," Toriel handed Gon a small, brick phone, although it fit snuggle in her own paw, it was nearly double the size of Gon's hand. "Use this whenever you see fit."

Gon crammed the thing inside his backpack then smiled, "Thanks!"

"Do I get anything?" Killua asked.

"I'm terribly sorry, that was my only phone, but I can get you some old candy."

"Yeah, I'll take that." Killua waited until Toriel was over an earshot away before turning to talk to Gon. "I think she likes you more than me."

"No, she's just looking out for you. I'm the one with the backpack after all."

"...I guess you're right."

Toriel scurried back to Killua with a handful of old candies, all of which Killua had never seen before in his life. "I do hope you like them!"

"Thanks Goat lady."

"Of course." Toriel turned to walk away, then abruptly paused at her door. "...please treat the monsters as you would any human." She entered into her house, leaving Gon and Killua to dwell on her statement.

"Treat the monsters as...humans? Killua, what is she talking about?"

"Keep thinking about it," Killua popped an old candy into his mouth. "You'll get it eventually."

"What?! That's not fair!"

"I'm just helping you out, Gon."

Toriel watched the two humans slowly fade away into the catacombs. 'Just one hour...' She kept thinking to herself. 'That's all I'll give them.'

A/N: As always, thanks for reading;)